Two point charges – 4 μc and 4 μc, constituting an electric dipole, are placed at (– 9, 0, 0) cm

Question

Two point charges \(-4 \ \mu \mathrm{c}\) and \(4 \ \mu \mathrm{c}\), constituting an electric dipole, are placed at \((-9,0,0)\ \mathrm{cm}\) and \((9,0,0) \ \mathrm{cm}\) in a uniform electric field of strength \(10^{4} \ \mathrm{NC}^{-1}\). The work done on the dipole in rotating it from the equilibrium through \(180^{\circ}\) is :

(1) 14.4 mJ

(2) 18.4 mJ

(3) 12.4 mJ

(4) 16.4 mJ

Answer 1

Correct option is : (1) 14.4 mJ

\(U = -\vec P.\vec E\)

Therefore W = 2PE

\( = 2\times 4\times 10^{-6}\times 18 \times 10^{-2} \times 10^4\) 

\( =144 \times 10^{-4}\)

\( = 14.4\ mJ\)